byrne



March 3, 1964 J. F. BYRNE PHOTOGRAPHIC COMPOSITION Filed Oct. 21, 1960 SILVER HALIDE MIXTURE LEAD HALIDE PREPARE HOMOGENEOUS MIXTURE AND DISPERSE IN ORGANIC COLLOID CARRIER INVENTOR.

JOHN F. BYRNE A 77' ORNE Y United States Patent 3,123,474 PHOTOGRAPHIC COMPOSITION John F. Byrne, Columbus, Ohio, assiguor, by mesne assignments, to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Filed Oct.21, 1960, Ser. No. 64 1M Claims. (Cl. 95-108) The present application is a continuation-in-part of my copending application Serial No. 737,831, filed May 26, 1958, now abandoned.

The present invention relates broadly to photographic sensitive films and more particularly to photographic films of the print-out type. The term print-out refers to that type-of photosensitive substance upon which a visible image is obtained after an initial exposure to light or electromagnetic radiation has been utilized to form a latent image, the visible image being obtained initially or simply by an additional exposure to such radiation. Th s additional exposure is known as latensification and is general in its application, including exposing the area upon which the initial image was formed as well as the surrounding background area to an added amount of radiation. Print-out emulsions are distinguished from development emulsions which require a development treatment such as a chemical development after initial exposure to produce a visible image, inasmuch as this image is produced by an additional exposure in print-out emulsions. The specific print-out papers coated with a film, comprising a dispersion or emulsion of the compositions of the present invention are particularly sensitive to a high intensity beam of light or other electromagnetic energy of either visible or invisible wavelength radiated across a portion of the area of the film. While the material of the present invention is particularly sensitive to such exposure, the background or non-exposed area is sufficiently stable to render a highly contrasting image upon subsequent latensification.

According to the present invention, a photosensitive silver halide is used as the basic sensitive ingredient of the composition, and a quantity of lead halide is added to the silver halide in order to improve the photo response thereof. The lead halide sensitizes the silver halide particularly to brief exposures, in the range of microseconds, from a high intensity source, but causes very little sensitization of the composition to relatively lower intensity radiation. A high degree of sensitivity to the trace coupled with a highly stable background produces a maximum contrast between the image and the background when applied to recording operations. The present invention provides this desirable combination of high image sensitivity and high degree of background stability.

The intensity of the radiation source utilized in latensification is not as critical with the sensitive mixtures of the present invention as it is with available compositions of the prior art. In other word-s, the accumulated quantity or intensity of illumination or radiation to which the sensitized paper is exposed during latensitication is not particularly critical. The latensification rate obtainable by an intense exposure to ordinary fluorescent lamp lighting conditions has been found to be satisfactory for the silver halide compositions of the present invention, while this intensity of light is generally too great for emulsions produced prior to the present invention.

The term halide as used throughout the specification is intended to encompass bromides and iodides, fluorides and chlorides being specifically excluded. Accordingly, the silver halide consists mainly of or entirely of silver bromide although the use of a mixture of predominantly silver bromide with a minor quantity of silver iodide has proved particularly useful.

In the early development of photography, print-out papers were relatively widely used for ordinary photographic purposes. With the advent of improved development emulsions, print-out emulsions fell into a more and more limited use and this situation continued until only recently when it was recognized that they possessed desirable properties for high speed recording such as oscillographic recording and the like. As an example, such a recording system is disclosed in the co-pending application of Mahoney et al., Serial No. 638,729, filed February 7, 1957, and entitled Recording Apparatus. Unfortunately, the sensitive papers and sensitive coating substances of the prior art are not entirely satisfactory for this recording purpose for a number of reasons. For example, it is generally true that the prior art papers which exhibit high sensitivity to an exposure of short duration to a high intensity beam tend to exhibit a correspondingly low degree of background stability. The printing -out or latensification procedure for these sensitive papers is highly critical and accordingly is exceedingly difficult if notimpossible to carry out. The latent image may be entirely lost during the subsequent latensification operation due to the fact that the background comes up or points-out too rapidly. In other cases a phenomenon known as reversal may occur, this being a darkening of the background which proceeds at a more rapid rate than darkening of the image or trace. In these situations, the trace may be temporarily or permanently lost. On the other hand, papers which exhibit a high degree of background stability tend to exhibit a correspondingly low degree of sensitivity tothe recording beam and accordingly the maximum writing speed (minimum exposure time) is far below that desired for use with modern recording instruments.

Hence, when it is attempted to produce a latent im'age upon a low sensitivity paper at an excessive rate for the paper, the image, if formed at all, will become lost against the background upon print-out.

In addition to these problems, it is also critical that the sensitive paper exhibit a certain degree of permanence in order that any record prepared thereon will have a 'sufficiently long and usable lifetime without losing its contrast. It is also desirable to have a sensitive paper which responds substantially uniformly to applied radiation without regard to varying intensities and different Writing speeds and yet which exhibits a substantially uniform degree of contrast against the background upon latensification. According to the present'invention, the sensitive films possess a sensitivity capable of writing in 'a wide range of speeds, including very slow speeds as Well as speeds ranging up to more than 50,000 lineal inches per second. In spite of the varying requirements relative to diiie'rent writing speeds, a uniform, relatively permanent, and highly contrasting image is produced upon latensificat'ion. Latensiiication may be accomplished through exposure to radiation within the sensitive range for the paper for 'a very short period of time. For example, several seconds or less under an ordinary fluorescent lamp is 'sufiicient to l-atensify or print-out the images or traces made on paper prepared in accordance with the present invention.

Accordingly, it is an object or" the present invention to provide improved print-out sensitive coating compositions which possess both a high degree of sensitivity to a trace recording along a portion thereof together with a high degree of background stability upon general latensification.

It is a further object of the present invention to provide print-out sensitive coating compositions which produce an image or trace which has a substantially uniform degree of contrast to the background, this contrast being relatively independent of the time the sensitive material has been exposed to a relatively intense and uniform light source.

It is yet another object of this present invention to provide a print-out emulsion which produces a latent invisible image after an initial exposure time in the range of microseconds, and which will print-out the latent image upon an exposure of general application of short duration. I

It is still a further object of the present invention to provide a photosensitive print-out sensitive coatmg composition which is exceedingly fast in its photographic response, which is substantially stable over a long period of time, and which may be retained for an indefinite period of time so long as it is not exposed generally to light or other electromagnetic radiation for extended periods.

Other and further objects will become apparent to those skilled in the art upon the study of the following specification, appended claims and accompanying drawings wherein,

FIGURE 1 is a schematic illustration of a preferred process for preparation of sensitive dispersions in accordance with the present invention; and

FIGURE 2 is a cross sectional view showing the sensitive material as a coating on a support member.

The exact theory of operation of the compositions of the present invention is not entirely understood. In silver halides generally, and in particular silver bromide, exposure to light produces elemental silver and free bromine, this phenomenon probably being carried out in accordance with the reversible equation shown below.

Applied to the present case, the free silver indicates the exposed area and a darkening of the area occurs. When the light or other electromagnetic radiation is removed, the reaction in general may tend to reverse and therefore proceed to the left with a consequent loss of indicated exposed area. Silver halide emulsions have long been employed in the photographic art, including silver bromide and silver bromo-iodide as employed in the present invention. The presence of lead halide is believed to prevent reverse reactions from occurring and hence increases stability. The useful halides of lead consist of both lead iodide and lead bromide. Lead iodide has been found to be markedly superior as a doping agent with silver halide to other compounds of lead, although lead bromide has also been found useful in the invention. The sensitivity achieved with lead bromide is essentially the same as that producible with lead iodide, however, both the iodide and bromide are superior by a considerable margin over other lead salts such as chloride, nitrate, acetate, etc. The writing speed of compositions containing other lead salts is lower, and the trace, if formed, tends to fade and in some cases is substantially assimilated into the background.

By way of theoretical explanation for the improvement obtained with lead halide additions as applied to compositions under consideration here, it will be appreciated that precise descriptions of the mechanisms involved are difiicult to set forth. It does appear however, that the lead halide functions as an acceptor for the bromine liberated by light energy on the silver bromide. It is believed that this could be by way of an oxidation of lead from a valence of +2 to a valence of +4, by a displacement of the iodide ion by bromine, or even by a combination of these phenomena.

Referring now to the lead halide additions, the relative proportion of lead halide added to the silver halide has been found to be beneficial only if held within certain limits. In cases where less than 0.1% of lead halide by weight has been added to the silver halide sensitive mixtures, a phenomenon known as reversal has occurred. In these instances, as previously indicated, the latent image is either temporarily or permanently lost or rendered without contrast against the background upon latensification. If lead halide is added in excess of about 20% by weight, the emulsion tends to become quenched and is substantially less sensitive. Thus, in the range between 0.1% and 20%, and in particular the range between 1% and 5%, there is found to be an optimum relationship between sensitivity of film and stability of background.

The lead halide additive, as noted above, performs substantially as a bromine acceptor, and hence there is no requirement that conventional bromine acceptors such as gelatin or the like be present in the compositions of the invention.

It has been found that a small percentage of silver iodide when added to the silver bromide enhances the sensitivity of the emulsions. In this connection, amounts ranging from about 1% to about 10% of the co-precipitated silver iodide have been found useful, and specifically about 5% of silver iodide appears to give optimum results. In this connection, it is believed that the silver iodide being present in the lattice sets up strains in the silver bromide lattice to such an extent that reduction of silver to the free metal is achieved more easily, and this reduction is rendered somewhat more stable in nature. Although the invention is operable using a single halide salt, e.g., AgBr, or with a mechanical mixture of AgBr plus AgI, the co-precipitated silver bromo-iodide is preferred.

The compositions of the present invention may be fur ther sensitized if desired, by adding from .01 to .2% (by weight based on total solids) of an organic sensitizer such as thiourea which is the preferred sensitizer for this composition. Thiocarbamide, thiose-micarbazide, paramethylamino phenol sulphate and mercapto succinic acid are useful and may be employed if desired.

Various inert carriers or binders, and particularly organic colloid carriers, may be employed in order to facilitate application and adhesion of the sensitive composition to paper in dispersion or emulsion from either aqueous compatible or aqueous incompatible carriers may be employed. In an aqueous system, pregelatinized dextrin gelatin, starch, dextrin, thickening agents such as seaweed extracts or polyvinyl alcohol are suitable. In the nonwater-soluble systems, silicones may be employed. The carriers do not in any way affect the photographic properties of the compositions, but are merely used to adhere the composition to the base material.

Among the various base papers or supports, one may employ almost any sort of cellulose paper so long as it is free from wood chip or the like. Conventional photographic base papers may be conveniently utilized.

Heat treating the coated paper when carriers other than gelatin have been used has been found advantageous in increasing top writing speeds and retarding the rate of background rise. In this connection, heating to a temperature of about 400 F. for a period of from 10 to 30 seconds produces beneficial results. Specifically a tem perature of about 400 F. for a period of about 20 seconds has been considered the optimum for compositions prepared in accordance with the present invention.

For exposure and latensification, the maximum sensitivity of the paper is found to be below about 5000 Angstroms, and mainly below about 4400 Angstroms. Various commercially available high intensity light sources may 'be conveniently employed for producing the trace image, such as for example the Osram lamp manufactured by Osram, Munich, Germany, as hereinafter identified in Example 1. By the term high intensity radiation reference is made to electromagnetic radiations having an intensity of about 10 ergs/sec./cm. or greater. In order to obtain a useful trace, this is preferably applied to the paper for a period of about 10- seconds or greater. Although lower intensity sources may be satisfactorily utilized, these sources may require substantially higher total energies inasmuch as the material exhibits a low intensity reciprocity failure.

While the sensitive films are particularly sensitive to radiations of relatively high intensity, they are also suitable for use at lower intensities, witha corresponding drop in writing speed. For latensification, a less intense source of light available generally across the extent of the paper is desired. Ordinary fluorescent lighting at close range is useful both inits intensity and its output wave lengths characteristic for latensification operation. For example, latensification may be carried out under the influence of illumination of the order of 75 foot-candles of cool-white fluorescent light.

In order to more particularly set out the features of the present 'mvention, specific examples of preparation are presented hereinbelow:

EXAMPLE 1 In the preferred embodiment of the present invention, the following preparation is recommended.

Preparation of Silver Nitrate Amount AgNO 187 gr. (1.1mol). H O (distilled) 500 cc. Nl-I (28-30% aqueous solution,

sp. gr. 0.90) 200cc.

The silver nitrate was Weighed and dissolved in the prescribed amount of distilled Water. This solution was heated to about 60 to 65 C. Then the ammonia solution was added with stirring until the solution cleared as the precipitate of silver oxide formed by the first added portions of the ammonia was redissolved.

Potassium Halide Solution Amount KI 9.13 gr. (0.055 mol). KBr 137 gr. (1.15 mol).

H2O (distilled) 500cc.

The potassium iodide was weighed carefully in order to insure precise control over the iodide content of the resultant silver halide mixture. The potassium halides were dissolved in the prescribed amount of water contained in two liter beakers which was set in a water bath. The water bath was provided with an inlet through which steam was introduced to heat the bath to about 95 C. The solution of potassium halide was stirred mechanical- :ly with the glass-rod stirrer driven by an air turbine.

Preparation of Silver Bromoiodide When the halide solution was hot (85 to 90 C.) the ammoniacal silver nitrate solution was added slowly in a steady stream to the reaction vessel. This Was done by pouring the silver solution slowly into a funnel to the outlet of which has been fused a short length (about 4 inches) of capillary tubing. The capillary jet delivered the silver solution at a rate of about 50 cc. per minute, so that the addition of silver was completed in about minutes. The iodide reacts preferentially because of its being less soluble than the silver bromide. In this connection, there may be considerable co-precipitation so that silver iodide is trapped in silver bromide crystals with the result that strained crystals of high sensitivity are formed.

Ammonia and potassium bromide act as solvents for the silver halides formed and promote crystal growth. Thus, in the presence of these solvents, the smaller silver halide crystals may dissolve and be re-deposited on the surfaces of larger crystals by a process known as Ostwald ripening. This process can occur during the slow precipitation step and also during the ripening step which folloWs the precipitation. The silver halide precipitate was ripened by maintaining the reaction vessel at 85 to 90 C. for a period of about minutes after all of the silver nitrate had been added, the mixture being stirred moderately with a mechanical stirrer during the ripening period.

After the ripening step, the silver halide mixture was filtered by suction on a Buchner funnel and was washed five times with distilled water.

It is not normally necessary to dry the silver halides after filtering and washing. If it is desired to dry the silver halides, this may be done in an oven at 220230 F. but can also be accomplished by exposure to low humidity air for about 24 hours.

Compounding of Print-Out Coating Mixture In addition to silver bromoiodide, the following ingredients were utilized in preparing a preferred mixture in accordance with the present invention.

Lead iodideto increase the print-out effect (and to suppress background during latensification).

Thiourea-to sensitize the halide mixture.

Dextrin-to bind the coating to the paper support.

Compound Amount Silver halide (as prepared hereinabove) 98 gr.

Lead iodide 2 gr.

Thiourea 0.1 gr. (dissolved in 10 cc. H O).

Dextrin (pregelatinized) 4 gr. (dissolved in 40 cc. H 0).

H 0 (distilled) 25 cc.

The ingredients listed above were placed in the eight ounce amber bottle of a ball-mill containing 200 grams of one-half inch porcelain pebbles. The bottle was rotated at about 100 r.p.m. for a period not exceeding about four hours, after which time a homogeneous mixture resulted. The mixture described above had a consistency which was found suitable for making flow-coated papers.

After milling it is convenient to mix the material prepared as above with an aqueous solution of a suspending agent to hold the silver halide particles in substantially uniform distribution for applying to paper in a subsequent coating operation. One such suspending agent found to be satisfactory is a sea-weed extract which was used in a one percent solution. It will be appreciated that this suspending agent should not adversely react with the sensitive materials. Sea Kern No. 402 is satisfac tory in this respect. After mixing into the suspending agent, the compositions are ready for application to the paper. In this connection various application techniques may be employed, such as transfer roller coating, dip coating using an air-knife to wipe off the excess upon emergence from the bath, or by conventional spreading using a doctor knife to control the thickness of the film. Although the thickness of the coatings to be applied to paper or other supports is dependent on the characteristics desired in the end product, it has been found that the composition disclosed above diluted to 600 cc. With water containing 1 percent Sea Kem 402 deposits useful coatings when applied in layers calculated to be in the range of from 2 to 10 mils in thickness. As the thickness of the Wet film is difficult to measure, it is somewhat easier to use the weight per unit area of solids deposited as a reference. About 1 gram of solids per square foot of the dried film appears to be satisfactory. The critical features are that the coating be uniform, flexible, and adherent to the base material. After application to the base paper, the coating Was dried and was subjected to a temperature of about 400 F. for a period of 20 seconds.

Attention is directed to FIGURE 2 of the drawings wherein there is illustrated a photosensitive paper 10 having a base support 11 and a sensitive coating 12. This coating was prepared as in Example 1 above.

The sensitive material prepared in accordance with Example 1 above and shown in FIGURE 2 was yellow in color and upon the desired exposure to light, a uniform medium dark brown image or trace having extremely fine edge definition was formed. Sensitive papers prepared according to this process were capable of writing speeds exceeding 45,000 inches per second when illuminated from a source having an intensity of about 10 ergs/-sec./ cm. Under the spectrum distribution obtainable from a high pressure mercury vapor arc lamp such as the Osram lamp manufactured by Osram, Munich, Germany, and identified as their model HBO-107/ 1, high pressure mercury lamp. A high proportion of this radiation is in the ultraviolet. A complete system for recording is described and disclosed in the aforementioned Mahoney et al. application.

EXAMPLE 2 A silver nitrate solution was prepared in accordance with the procedures of Example 1, and a potassium halide solution was prepared as follows.

Compound: Amount KBr 143 gr. (1.2 mole). H O (distilled) 500 cc.

The potassium bromide was dissolved in the prescribed amount of water in a two liter beaker set in a water bath as in Example 1 above. The ammoniacal silver nitrate solution was added to the potassium bromide in accordance with the procedure set forth in Example 1 above. The remaining steps in this process were likewise in accordance with the procedures outlined in Example 1 above.

This material was substantially the same as the material prepared in accordance with the Example 1 above, except that the K1 has been omitted from the potassium halide solution. It is somewhat less sensitive however and therefore was not capable of use in such high speed recording operations.

EXAMPLE 3 Identical techniques, preparations and compositions were followed as in Example 1, with the exception that 1% of lead iodide was added to the composition rather than the 2% as added therein. The resultant material provided a good recording paper capable of recording a distinct trace at writing speeds in the range of 50,000 inches per second and more under the identical conditions set forth in Example 1 herein. This trace is also uniform in color and contrast upon latensification.

EXAMPLE 4 Identical techniques, prepartions and compositions were followed as in Example 1 above with the exception that 10% rather than 2% of lead iodide was added to the composition. This resulted in a recording paper capable of recording a uniform distinct trace at speeds in the range of 35,000 inches per second under the identical conditions as set forth in connection with Example 1. A weak trace was obtainable at speeds in range of 50,000 inches per second.

EXAMPLE 5 Identical techniques, preparations and compositions were followed as in Example 1 above with the exception that 20% rather than 2% of lead iodide was added to the composition. This resulted in a recording paper capable of recording a weak trace at speeds in the range of 25,000 inches per second under the conditions as specified in EX- ample 1.

EXAMPLE 6 Identical techniques, preparations and compositions were followed as in Example 1 above with the exception that 50% rather than 2% of lead iodide was added to the composition. This mixture exhibited only slight sensitivity to the recording beam as specified in Example 1.

In any of the foregoing examples, if desired, the silver halides may be precipitated in cold water or even ice water. In addition, the crystal ripening and milling processes may be dispensed with, although the characteristics of the material, for the purposes of this disclosure may be affected adversely to some extent.

It will be appreciated from the foregoing description that the present invention makes possible the production of sensitive papers capable of giving a sharp visible image at writing speeds of up to 50,000 in./sec. The latent image becomes visible almost instantaneously under fluorescent light; say within 5 seconds after exposure, and maintains good contrast against the background for extended periods of time. Such papers find extensive use in modern recording instruments.

EXAMPLE 7 The preceding examples are illustrative of preferred compositions using lead iodide as the doping material. However, as previously noted lead bromide has also been found useful in the invention. Results obtainable with lead bromide are nearly the same as those obtained with lead iodide. Some variation in sensitivity of both the background and of the trace produced is noticeable, however, the use of lead bromide as well as the use of lead iodide is considerably superior to the use of other lead salts such as nitrates, chlorides, acetates, etc.

The procedure used in Example 2 was followed for the preparation of the silver bromide up to the stage of cornpounding the print-out coating mixture. Compounding was made according to the following schedule.

Compound Amount Silver bromide 100 grams (as prepared hereinabove). Lead bromide 0.5 gram. Dextrin (pregelatinized 1 gram. Distilled water 25 grams.

This mixture was then ball milled as in Example 2 and produced a mixture of desirable consistency for flow coating paper. Paper prepared in this manner had writing speeds approximately as fast as those prepared using lead iodide as the doping material.

EXAMPLE 8 A solution (1) of potassium bromide and water was prepared with the following concentration.

Distilled water cc 39 Potassium bromide grams 13.9

A second solution (2) of silver nitrate and lead nitrate was prepared having the following composition.

Distilled water cu. cm" 55 Silver nitrate grams 16.3 Lead nitrate do 1.1

Solution 2 was added with stirring to solution 1. The resulting precipitate was filtered and washed with distilled water. The resulting material was applied to a paper as in Example l. Writing speeds of 30,000 inches per second were obtained. However, the image could only be made visible after exposure if the paper had been heated prior to or during the post exposure period. The heating found most desirable was at 325 F. for 20 seconds.

EXAMPLE 9 A solution (1) of silver nitrate, lead nitrate, and water was prepared with the following concentration.

Compound: Amount Silver nitrate grams 272 Lead nitrate do 26.5 Distilled water cc 500 A second solution (2) of potassium bromide was prepared having a concentration of 240 grams of potassium bromide in sufiicient water to make a volume of 525 cc. This second solution is equivalent to 3.84 molar potassium bromide.

Solution 1 was added to solution 2 with stirring, ripened to give a total time of 30 minutes at C., filtered, and Washed three times with distilled water. The wet precipitate was used at once to make a coating mixture as follows:

300 g. wetness) AgBrPbBr (20:1=molAg:molPb 60 cc. of 5% aqueous pregelatinized dextrin solution This composition was ball milled for 23 hours, and then made into a coating mixture utilizing a small quantity of thiourea in a quantity as indicated hereinabove. A coating prepared from this composition Was found to have a sensitivity approximately equal to those of other solutions of the above examples.

Other and further modifications may be employed without departing from the spirit and scope of the present invention. It will be appreciated of course, that the foregoing examples are given for purposes of illustration only and there is accordingly no intention to limit the scope of the present invention to these particular modifications.

I claim:

1. A photosensitive print-out composition comprising a photosensitive substance, said substance consisting essentially of from about 0.1% to 20% by weight lead halide, the balance of said substance being a precipitated Washed silver halide, said lead halide selected from the group consisting of lead bromide and lead iodide, said silver halide containing up to mol percent of silver iodide, the balance being silver bromide.

2. A photographic print-out composition comprising a photosensitive substance, said substance consisting essentially of from about 0.1% to by weight lead halide, the balance of said substance being silver bromide, said lead halide selected from the group consisting of lead bromide and lead iodide.

3. A photographic print-out composition comprising an inert carrier having dispersed therein a photosensitive substance, said substance consisting essentially of about 2% by weight lead iodide, the balance of said substance being a precipitated washed silver bromide.

4. A photographic print-out composition comprising an inert organic carrier having dispersed therein a photosensitive substance, said substance consisting essentially of from greater than 0.1% up to about 20% by weight lead iodide, the balance of said substance being a precipitated Washed silver halide, said silver halide containing up to about 10 mol percent of silver iodide, the balance being silver bromide.

5. The photographic print-out composition of claim 4 being further characterized in that the photosensitive substance contains greater than about 1% up to about 5% by weight of lead iodide homogeneously dispersed therein.

6. A photographic print-out composition comprising an organic colloid carrier having dispersed therein a photosensitive substance, said photosensitive substance consisting essentially of 2% by Weight of lead iodide, the balance of said substance being a washed precipitated silver halide, said silver halide containing up to 5 mol percent silver iodide, the balance being silver bromide.

7. A photographic print-out emulsion sensitive to high intensity radiation of short duration including a film of photosensitive substance dispersed in an organic colloid carrier, said photosensitive substance consisting essentially of from about 1% to about 5% by weight of lead iodide, the balance of said substance being silver halide,

10 said silver halide containing up to 10 mol percent silver iodide, the balance being silver bromide, said photosensitive substance having added thereto from .01% up to 0.2% by weight thiourea.

8. A photographic print-out emulsion sensitive to high intensity radiation of short duration including a film of photosensitive substance dispersed in pregelatinized dextrin, said photosensitive substance consisting essentially of from about 1% to about 5% by Weight of lead halide, the balance of said substance being silver halide, said lead halide selected from the group consisting of lead bromide and lead iodide, said silver halide containing up to about 10 mol percent silver iodide, the balance being silver bromide.

9. A process for the production of photographic printout emulsions sensitive to high intensity radiation of short duration and including an inert colloid carrier having a photosensitive substance consisting mainly of silver halide and lead halide dispersed therethrough, said process comprising co-precipitating a slurry of silver halide salts wherein from 90 mol percent to 99 mol percent of the silver halides is silver bromide and the balance silver iodide, maintaining said slurry at a temperature of between and C. for a period of about 20 minutes, washing said precipitate, dispersing an amount of lead halide of the class consisting of lead bromide and lead iodide into said silver pericipitate in an amount equal to from 0.1% up to about 20% by weight of said lead halide-silver halide mixture, and dispersing said photosensitive substance in an inert colloid carrier.

10. A process for the production of photographic printout paper sensitive to high intensity radiation of short duration and including a support element coated with an inert colloid carrier and having a photosensitive substance consisting mainly of silver halide and lead halide dispersed therethrough, said process comprising co-precipitating a slurry of silver halide salts where at least 80 molar percent of the silver halide is silver bromide and the balance silver iodide, washing said precipitate, dispersing an amount ranging between about 0.1% and up to about 20% by weight of lead halide based on the weight of the silver halide-lead halide mixture into said silver halide, said lead halide selected from the group consisting of lead bromide and lead iodide, forming a dispersion of said silver halide and lead halide in an inert colloid carrier, coating a support member with a film of said dispersion, and heating said film to a temperature of about 400 F. for a period between 10 to 30 seconds.

References Cited in the file of this patent UNITED STATES PATENTS 2,816,029 Jones Dec. 10, 1957 2,843,490 Jones July 15, 1958 3,039,871 Scott June 19, 1962 3,047,392 Scott et a1 July 31, 1962 

1. A PHOTOSENSITIVE PRINT-OUT COMPOSITION COMPRISING A PHOTOSENSITIVE SUBSTANCE, SAID SUBSTANCE CONSISTING ESSENTIALLY OF FROM ABOUT 0.1% TO 20% BY WEIGHT LEAD HALIDE, THE BALANCE OF SAID SUBSTANCE BEING A PRECIPITATED WASHED SILVER HALIDE, SAID LEAD HALIDE SELECTED FROM THE 